The DNC said it blocked the campaign from the system after members of Sanders' staff collected information from Hillary Clinton's data. Officials said that the information was accessible because the vendor that runs the system ran a software patch that allowed all users to access other campaigns' data.

The Sanders campaign fired its top data staffer, but in response to the breach, the DNC temporarily suspended Sanders' campaign from the database.

The campaign filed a lawsuit in federal court late Friday to regain access to the database.

"It is our information and the information of all of these volunteers and the people who support our campaign, not the DNC's," Sanders campaign manager Jeff Weaver said. "In other words, by their action, the leadership of the Democratic National Committee is now actively attempting to undermine our campaign."

DNC Chairwoman Debbie Wasserman Schultz said she wants to know whether the Sanders campaign used any of Clinton's data.

"When we receive this report from the Sanders campaign, we will make a determination on re-enabling the campaign's access to the system," she said in a written statement.

The Clinton campaign said, "We are asking that the Sanders campaign and the DNC work expeditiously to ensure that our data is not in the Sanders campaign's account."